Value of Damage Control with Foliar Fungicide in Soybean Production in Tennessee

Abstract

Core Ideas Annual application of foliar fungicide in continuous soybean increased yields. Breakeven soybean price for applying a foliar fungicide ranged from US$0.13 to $0.27kg−1. Results suggest a high likelihood that foliar fungicide application is profitable. With the expansion in soybean (Glycine max L.) land area in the Southeast, producers are wondering how to profitably manage the disease frogeye leaf spot (FLS) (Cercospora sojina); however, little is known about the profitability of using foliar fungicide on soybean infected with FLS. We determined the effect of total water applied, growing degree days, and foliar fungicide treatment on FLS severity and yield of soybean in maturity group (MG) III, IV, and V. A two‐stage severity/treatment outcome model was estimated and results were used to calculate the breakeven price of soybean for applying a foliar fungicide by MG. Data came from an 11‐yr soybean fungicide (quinone) experiment in Tennessee. Applying a foliar fungicide to soybean in a high disease pressure location reduced FLS severity and increased yields for each MG. Annual application of foliar fungicide in continuous soybean was found to increase yields by 475 kg ha−1 for MG III, 321 kg ha−1 for MG IV, and 408 kg ha−1 for MG V. The breakeven price of soybean, for applying a foliar fungicide, ranged from US$0.13 to $0.27 kg−1 for all MGs, depending on the application cost. A profit‐maximizing producer would apply a foliar fungicide as part of the annual production practices to manage FLS since the soybean price has historically been above the breakeven price. Results from this study will inform Tennessee and southeastern producers on the profitability of spraying soybean with a foliar fungicide to manage FLS.